The present invention relates generally to clock-switching circuits and methods and, more particularly, to security-compliant clock switching.
The timing of the functions performed by an integrated circuit (IC) is regulated by a clock. As integration and system complexity has increased, ICs have employed multiple clocks running at different frequencies so that each particular IC function can be clocked at an optimal rate for that particular function. A clock switch is a circuit used to change the system clock when appropriate or necessary. Some clock switches enable the host IC to switch the system clock between an externally generated clock (referred to as an external clock) and an internally generated clock (referred to as an internal clock).